1. Field of the Invention
The present invention relates to ink-jet recording methods and recording apparatuses capable of providing high-quality images on a recording medium, and in particular, to an ink-jet recording method for discharging a printing-characteristic improving liquid causing recording ink on a recording medium and coloring material in the recording ink to become insoluble or to aggregate, and a recording apparatus for practicing the ink-jet recording method, which both enable high-speed printing. The ink-jet recording method and the apparatus are applicable specifically to office equipment with the recording apparatus as output means, such as printers, photocopiers and word processors, and manufacturing equipment such as textile printers for printing on textiles.
2. Description of the Related Art
The ink-jet recording technique is conventionally used in printers, photocopiers and so forth because of that technique has advantages such as low noise, and reduced-size recording units.
When an image is formed on a recording material of the type known as "plain paper" using a recording apparatus employing ink-jet recording, the image formed is not water-fast; the image may run if it becomes wet. When a color image is formed by ink-jet recording, it is practically impossible to produce a highly concentrated image without feathering and without blurring between colors. Thus, a color image having the desired image durability and quality cannot be obtained.
In order to improve the water resistance of an image, ink having waterproof coloring material has recently been used for practical use. However, since in principle the ink still has insufficient water resistance, and becomes almost insoluble in water after it is dried, the ink easily clogs recording-head nozzles. Accordingly, to prevent such clogging, the recording apparatus structure must be complicated.
A number of techniques for improving the durability of a recording medium have been disclosed. In Japanese Patent Laid-Open No. 53-24486, there is disclosed a technique for changing dye into color lake to fix by the postprocessing of dyed material in order to improve the dyed material durability against humidity.
In Japanese Patent Laid-Open No. 54-43733, there is disclosed a method in which recording is performed by the ink-jet recording method using two or more components for increasing film-formation ability in touching mutually at normal temperature or when they are heated. This provides a print having a film strongly adhered to the recording medium when the components on the recording medium are caused to touch one another.
In Japanese Patent Laid-Open No. 55-150396, there is disclosed a method for providing a waterproof agent for forming color lake after performing ink-jet recording with water-dye ink.
In Japanese Patent Laid-Open No. 58-128862, there is disclosed an ink-jet recording method for recording by sequentially providing recording ink and processing liquid after recognizing in advance the position of an image to be recorded. According to the ink-jet recording method, recording is performed with the processing liquid after using the recording ink, the processing liquid being applied to the recording ink previously provided, or the recording ink being applied to the previously provided processing liquid before providing fresh processing liquid thereon.
In the above Japanese Patent Applications there are not disclosed restoration means for maintaining discharging reliability, a head structure, a container structure, printing modes for improving a recording image quality, and so forth, which are characteristic in the ink-jet recording apparatus.
In addition, images can be printed at high speed using a bi-directional printing method which scans by moving a carriage in two directions. Such bi-directional printing causes an image-quality difference due to the shift in the position of ink provided by bi-directional scanning, and a color difference due to the different order in which the several different color inks are applied.
When a recording head for the processing liquid and a recording head for the ink are arranged in the main-scan direction, the order in which the processing liquid and the ink are provided is reversed from one direction of scan to the other. The processing liquid often causes the ink color to change. The ensuing color variation is readily seen when one compares the case where recording is performed by applying the processing liquid before the ink and the case where recording is performed by applying the ink before the processing liquid.
For the foregoing reasons, when part of an image printed in one direction and an adjacent part of the image is printed in another direction, the color and image-quality difference between the adjacent parts appear strongly, which disadvantageously causes noticeable image-quality deterioration.
According to Japanese Patent Laid-Open No. 2-233275, a break (blank image portion) in an image is detected so that a region to be printed in another direction is not adjacent to the break, which enables bi-directional printing. In this method the printing direction is not reversed unless the break is detected. Printing continues in the same direction as the previous printing direction until the break is detected. One example is shown in FIG. 10. Region a' is printed in the direction from left to right (the "forward" direction). Since a break is not detected between regions a' and b', region b' is printed in the same direction in which region a' was printed. A break exists between regions b' and c'. Thus, when region c' is printed, a carriage moves in the direction opposite to the direction in which the previous region was printed. In other words, region c' is printed in the direction running from right to left (the "backward" direction). Since a break is not detected between regions c' and d', region d' is printed in the same direction in which region c' was printed.
The above method is effective in reducing the difference between the forward-printed color and the backward-printed color or a shift in the position of printed ink and performing the bi-directional printing.
In addition, the present inventors have found that, when a combination of a material having an increased amount of a surface active agent and another material having a reduced amount of a surface active agent, or no surface active agent, is selected from combinations of ink and a print-characteristic improving liquid including a material for improving print characteristics (such as water resistance) of the ink when the ink is provided to a recording medium, an irregular image is generated at the region between scans due to the order of shooting the ink and the print-characteristic improving liquid. The phenomenon and the mechanism of this occurrence will be described below.
The main cause of the irregular image at the region between the scans is a phenomenon in which the concentration of the ink has a distribution such as to form a whitish portion, which is hereinafter referred to as a "white blur" phenomenon. It is thought that the white blur phenomenon is caused by the surface active agent.
FIGS. 8A to 8D illustrate the white blur phenomenon caused by the distribution of the ink concentration on an image border.
FIG. 8A shows an example in which a liquid-A printing region and a liquid-B printing region are mutually in contact. Ink with a relatively high amount of surface active agent is used as liquid A, while ink with a reduced amount of the surface active agent is used as liquid B. As shown in FIG. 8A, the white blur phenomenon occurs in the liquid-A printing region.
In general, adding a surface active agent reduces a liquid's surface tension and increases the liquid's permeability. Ink having high surface tension and low permeability is unlikely to produce the phenomenon of "feathering" in which ink expands along fibers of paper, which means the border between printed part and non-printed part will be clear. Accordingly, ink having low permeability is frequently used as black ink for printing characters. In contrast, ink to which increased amounts of surface active agent have been added has low surface tension and high permeability. Such ink is likely to cause feathering but quickly permeates the recording medium. Thus, this ink causes little ink mixing (called "bleeding") at the contact border between different colors, and is preferably fixative. This type of ink is frequently used as an ink having a color other than black. In many cases, liquid having high permeability is used as the print-characteristic improving liquid in consideration of fixation improvement, discharge characteristics, and so forth.
FIGS. 8B to 8D show the mechanism by which white blur is thought to occur. As shown in FIG. 8C, when liquid (ink) A having low permeability contacts liquid (ink) B having low permeability, the liquids having been applied to a recording medium as shown in FIG. 8B, a surface active agent included in liquid B reaches the edge of liquid A which in contact with liquid B. As a result, liquid A has a region (region 11) where an increased amount of surface active agent is added and there is also a region (region 12) where the amount of surface active agent is reduced. The influence of the inflowing surface active agent causes liquid A, which originally had high surface tension and low permeability, to have low surface tension and high permeability. The high surface tension-portion (region 11) in liquid A concentrates at the center of the liquid-A drop due to the high surface tension itself. Accordingly, the concentration of liquid A has a distribution. Region 11 has a high concentration, while region 12 has a low concentration. The influence of the surface active agent causes liquid A in region 12 to quickly permeate the recording medium, with the low concentration of region 12 being unchanged. As a result, coloring material in the liquid A hardly remains on the surface of the recording medium, and the surface looks whitish, as shown in FIG. 8D.
The white blur occurs not only in the contact border in the main-scan direction in which a recording head and a recording medium are relatively moved in a recording mode but also between different rows in the sub-scan direction in which the recording head and the recording medium are relatively moved in a non-recording mode.
In addition, the occurrence of the white blur is not limited to the case that the liquid-B printing region is formed with only a single liquid. For example, the white blur occurs also when a liquid with a surface active agent and a liquid without a surface active agent are simultaneously put on the liquid-B printing region.
FIGS. 9A to 9E show the occurrence of white blur when black ink (liquid-A type without a surface active agent) and a print-characteristic improving liquid (liquid-B type with a surface active agent) are simultaneously applied.
FIG. 9A schematically shows a monochrome-printing recording head provided with a print-characteristic-improving-liquid (S) discharge outlet represented by diagonal lines and a black ink (Bk) discharge outlet represented by black. The recording head moves on a recording medium in the directions denoted by arrows so that an image is recorded on the recording medium.
FIG. 9B shows a case in which the recording head shown in FIG. 9A performs recording for two rows by moving from right to left on a print region. In this case, a black record image and a print-characteristic-improving-liquid record image overlap. In other words, the print-characteristic improving liquid is ejected after the ink has been ejected. When recording with the print-characteristic improving liquid is performed after performing recording with the ink, white blur is generated on the border between the print regions as shown in FIG. 9B.
Region 21 is an area formed by the previous scan, in which the ink and the print-characteristic improving liquid mix, and the effect of the print-characteristic improving liquid causes coloring material in the ink to be insoluble or aggregate. Since the print-characteristic improving liquid has been applied in region 21, its surface active agent exists. With the recording head moving from right to left, the ink is initially ejected onto the recording medium, and after a lapse of a predetermined time determined by the head width and the moving speed of a carriage, the print-characteristic improving liquid is ejected to form an area where the black ink and the print-characteristic improving liquid mix. Region 22 is a region where nothing is printed. Region 23 is a print region where only the ink is used. Regions 24 is a print region where both the print-characteristic improving liquid and the ink are used, similar to region 21.
FIG. 9D schematically shows a condition just before the white blur seen in FIG. 9B occurs, namely, the same condition as shown in FIG. 8B in the section taken on line 9D--9D shown in FIG. 9B. Region 21 has a large part of the surface active agent included in the print-characteristic improving liquid. Since only the black ink forms region 23, no surface active agent is included in region 23. Region 21 and region 23 come into contact, and the surface active agent in region 21 moves to region 23. Consequently, the distribution (white blur) of the ink concentration is generated on the edge of region 23 as shown in FIG. 9B. In other words, the section shown in FIG. 9D changes consequently to the condition shown in FIG. 8C.
After white blur is generated in black ink in a region, even if a print-characteristic improving liquid is ejected in the region, the white blur cannot be improved. Instead, the effect of the print-characteristic improving liquid causes coloring material to be insoluble or aggregate, with the distribution of the ink concentration unchanged.
FIG. 9C shows the reverse of the case shown in FIG. 9B in which the recording head shown in FIG. 9A performs recording for two rows by moving from left to right. In this case a black record image and a print-characteristic-improvement-liquid record image overlap. In other words, the print-characteristic improving liquid is ejected before the ink. When recording with the print-characteristic improving liquid is performed before performing recording with the ink, white blur as shown in FIG. 9B is not generated on the border between the print regions.
Region 25 shown in FIG. 9C is an area formed by the previous scan, in which the ink and the print-characteristic improving liquid mix. Since the print-characteristic improving liquid is included in region 25, its surface active agent is also included. With the motion of the recording head from left to right, the print-characteristic improving liquid is initially ejected, and after a lapse of a predetermined time, the black ink is ejected to form a region where the black ink and the print-characteristic improving liquid mix. Region 26 is, similar to region 25, a print region in which both the print-characteristic improving liquid and the ink are used. Region 27 is a print region where only the print-characteristic improving liquid is used. Region 28 has no recording.
FIG. 9E schematically shows the section taken on line 9E--9E shown in FIG. 9C.
The print-characteristic improvement liquids have been ejected in both regions 25 and 27. Thus, surface active agents are present in regions 25 and 27.
The black ink is applied in the print region (region 27) where only the print-characteristic improving liquid is used. However, unlike the case shown in FIG. 9B, when the black ink reaches the recording medium, the print-characteristic improving liquid has been already applied. Accordingly, the concentration of the surface active agent has no distribution, and when the ink comes into contact with the print-characteristic improving liquid, the coloring material becomes insoluble or aggregates quickly, so that white blur cannot occur.
The foregoing cases have been described in connection with monochrome printing. However, a similar phenomenon also occurs when color ink not having a surface active agent is selected.
As described above, the present inventors have found that, when ink is ejected before ejecting a print-characteristic improving liquid, the image quality of a border in contact with a region including the print-characteristic improving liquid may deteriorate remarkably in the main-scan direction and the sub-scan direction.